Gas pooled on piston prior to starting

[deany41]

Gas and gasohol have a much lower boiling point than water. An engine oil temp at the pan is typically close to 300*F. In addition, there is an exhaust crossover in your intake manifold. So, after heating up the engine and you park the car, heat migrates straight up the carb. That heat boils your gas, causes the needle and seat to open, and the liquid goes down the intake.

If your fuel line pressure is too high, the needle isn't designed to stop it, so your bowl floods. If the gas keeps coming, it simply dumps down your intake. Normal fuel pressure and a good rebuild kit will remedy this problem. Keep your pressure under six psi. - Dave

OK ...I think I get it. The exhaust crossover in the intake manifold explains a lot. After doing some reading, apparently some are blocking that port to avoid the problem with the heat soak/boiling gas problem in there rods. Will be going to Helena NAPA today to get a pressure regulator and power valve. Thanks for the explanation.

[simplyconnected]

The exhaust crossover in your intake is run by your heat riser valve (in your RH exhaust manifold).

When the engine is cold, reach down to the end of the passenger's side exhaust manifold and see if the valve operates freely. When they freeze up, it's usually in the closed position. That sends most of the exhaust gasses over to the LH side through your intake manifold. This quickly warms your engine in cold winter weather. When the exhaust temp is hot, a bi-metal spring (it looks like a large clock spring) on the outside of that valve relaxes, which keeps the valve open. - Dave

[Tbird1044]

Today, I did a wet test on the float levels. BTW, the secondary float bowl was close to full and the Primary float bowl was empty when I pulled the top. It had been about 2 days since I ran the car. I Pulled the top and cranked the car over to fill float bowls. I checked the levels and they were pretty close to the dry preset. Then I started the car, ran it, and check again. The Primary was a bit high and the secondary was right on. Never ran the engine long enough to develope any heat for "heat soak" problems. Engine was basically cold. I set the top back over the carb and waited about an hour and again checked the float levels. The primary had dropped about 3/16" and the secondary was still right on spec.
Tomorrow, I'm going to buy another rebuild kit and put all new gaskets, power valve etc in it and see if it solves this problem. I'm not totally convinced this will solve the problem, but I'll try it one more time.
Nyles

[deany41]

The exhaust crossover in your intake is run by your heat riser valve (in your RH exhaust manifold).

When the engine is cold, reach down to the end of the passenger's side exhaust manifold and see if the valve operates freely. When they freeze up, it's usually in the closed position. That sends most of the exhaust gasses over to the LH side through your intake manifold. This quickly warms your engine in cold winter weather. When the exhaust temp is hot, a bi-metal spring (it looks like a large clock spring) on the outside of that valve relaxes, which keeps the valve open. - Dave

REALLY appreciate this information. I actually removed the butterfly on this valve since it was hopelessly froze into position. Since I don't pull the car out of storage until June and back again in October it shouldn't be a problem. I would think however that the heat still concentrates through this bi pass when engine is shut down which adds to potential heat soak.

[Tbird1044]

Well, the saga continues. I rebuilt the carb, and put in all new gaskets, power valve, secondary diaphragm etc. etc. etc. I put the carb back on the car and did a wet float level check, with the car running, just to verify proper setting. All good. Car actually ran pretty good, but the idle needle valves are closed a lot more than specs. When the car is running in the garage, it does NOT get nearly as smelly as it used to. I did not put all the screws into the top of the carb so I could pull it and physically check the gas level in the primary float bowl. After about 24 hours, the fuel level dropped about 1/2". I pulled the carb back off of the car and again disassembled it to methodically look at everything and trace any carb ports to see where they all go. I put the carb back together and set it on the bench with fuel in the primary bowl. After about 16 hours, the fuel dropped about a 1/4". There was absolutely NO indication of leakage anywhere. Evaporation seems to be a bit excessive at that rate.
I put the carb back on the car today and ran it and all seemed good. I still do not have the top secured to the carb so I can check the fuel level vs. time and see what is going on. So far, it looks like the level is still dropping, but not near as fast as it was before I rebuilt it.
I hate to give up, but the Edelbrock is looking better all the time.
Nyles

[scumdog]

Why worry about that level of evaporation? (Even the Edelbrock will probably have the same issue I suspect!)

Just put the rest of the screws in and drive the 'bird and enjoy it.

fyi, if my 'bird sits for much more than a week it takes about 2 or 3 five-second bursts on the starter to get enough fuel back up to the carb to get the car running, after that it's all good - until the next time I leave it sitting for a week+!

[jopizz]

As far as whether or not to replace your carb is dependent on how much you like originality. I have an Edelbrock 1406 on mine and as much as I like a totally original car I wouldn't go back to the 4100 for anything. I also had a problem of the carb going dry after a few days. It hasn't been an issue with the Edelbrock so I can only surmise that it has something to do with the design of the carburetor and the new blend of fuels.

John

[deany41]

Well, the saga continues. I rebuilt the carb, and put in all new gaskets, power valve, secondary diaphragm etc. etc. etc. I put the carb back on the car and did a wet float level check, with the car running, just to verify proper setting. All good. Car actually ran pretty good, but the idle needle valves are closed a lot more than specs. When the car is running in the garage, it does NOT get nearly as smelly as it used to. I did not put all the screws into the top of the carb so I could pull it and physically check the gas level in the primary float bowl. After about 24 hours, the fuel level dropped about 1/2". I pulled the carb back off of the car and again disassembled it to methodically look at everything and trace any carb ports to see where they all go. I put the carb back together and set it on the bench with fuel in the primary bowl. After about 16 hours, the fuel dropped about a 1/4". There was absolutely NO indication of leakage anywhere. Evaporation seems to be a bit excessive at that rate.
I put the carb back on the car today and ran it and all seemed good. I still do not have the top secured to the carb so I can check the fuel level vs. time and see what is going on. So far, it looks like the level is still dropping, but not near as fast as it was before I rebuilt it.
I hate to give up, but the Edelbrock is looking better all the time.
Nyles

Pretty much did the rebuild carb kit thing yesterday to correct the fuel dumping into the manifold and to get rid of the gas smell. I also put in a fuel pressure regulator. I don't know what did the trick but the smell and the fuel smell is greatly reduced. In addition I did not have a noticeable fuel drop in the bowls after 24 hours.

Noticed that the Napa kit had a different style power valve than the one I replaced. They shipped two styles of washer seals. One that apparently fit the power valve that was included which had slots on the bottom for fuel discharge (small picture) which uses a washer style seal and a seal that was used for the type that has holes (shown with the valve). I inadvertantly put the wrong one on the kit power valve and noticed it covered the slots. Dug around in the kit and discovered a round washer that seemingly fit. It also had a different style bottom carb gasket which is entirely open rather than sealing around the 4 round manifold holes. Sort of clears the way for the vacuum hole to the power valve.

[Tbird1044]

It's amazing, isn't it, that they give you 3 different gaskets for the same part but never tell you which one should be used in your application. My carb is definitely better, but I am still losing level in the primary float bowl. Not near as bad as it was, but it seems more excessive than just evaporation. I even put gas in a glass on my bench to compare evaporation rates on the bench to the carb. I was actually surprised by the evaporation out of the glass. Well, as long as I am not dumping raw gas into the intake after a hot stop and flooding the engine, like so many others, I will probably install an electric pump to prime the dry carb after it has been sitting a while. I feel like I'm surrendering to Autolite, but have run out of ideas.
Nyles

[scumdog]

I will probably install an electric pump to prime the dry carb after it has been sitting a while. I feel like I'm surrendering to Autolite, but have run out of ideas.
Nyles

I don't mind having to givee the key a twist 3 or so times for 5 seconds or so until fuel gets pumped up into the carb.

I know then that oil has also started being pumped around the motor before it actually starts.